The subject matter disclosed herein relates generally to systems and methods for computed tomography (CT) imaging, for example to systems and methods for perfusion studies using CT imaging.
In CT imaging, an X-ray source may be rotated around an object to obtain imaging information. X-rays from the source attenuated by the object may be collected or detected by a detector and used to reconstruct an image. Patient radiation dose from the X-ray source is a concern in clinical practice.
In conventional perfusion studies, a large number of scans may be acquired, or the time of exposure to X-rays may be relatively large, resulting in relatively high X-ray doses for perfusion exams relative to other types of CT exams. For example, in traditional CT perfusion exams, for each anatomical location-of interest a series of CT scans are taken on a patient sequentially over a period of time that covers the pre-contrast phase, contrast uptake phase, and contrast washout phase. The contrast uptake and washout phase information are retrieved by measuring the contrast in the artery and vein regions of interest in the series of reconstructed image volumes. There may be as many as 20 or more scans in total in one perfusion example. Therefore, the X-ray dose in traditional CT perfusion exams may be significantly higher than other types of CT exams.
Recently, some studies have indicated that CT perfusion studies may be accomplished using only three scans taken at appropriately selected phases, namely a pre-contrast phase, an arterial phase, and a delayed phase. Accordingly, if arterial and delayed phases can be efficiently estimated without requiring reconstructed images, most of the scans of current or traditional perfusion protocols may be eliminated. Elimination of many or most of the scans of current or traditional perfusion protocols my simplify the perfusion exams and save a significant amount of X-ray radiation dose to a patient. Or alternatively, even for traditional perfusion studies where a series of scans are collected, sampling intervals may be dynamically adjusted based on the phase of the contrast uptake. For example, the arterial phase may be sampled at a higher frequency than the washout phase. However, the identification of the phases (e.g., arterial phase) or portions thereof (e.g., onset of arterial phase, transition from arterial phase to washout phase) using certain known approaches is estimated before a perfusion study is initiated. These estimations often suffer from inaccuracy, due, for example, to differences between patients.